Hydrogen embrittlement is a complex phenomenon, involving several lengthand timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement.

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Hydrogen embrittlement is, and has been for over a century, a prominent issue within many sectors of industry. Despite this, the mechanisms by which hydrogen embrittlement occurs and the suitable means for its prevention are yet to be fully established. Hydrogen embrittlement is becoming an ever more pertinent issue. This has led to a considerable demand for novel hydrogen embrittlement resistant alloys, notably within the bearings industry. This paper provides an overview of the literature surrounding hydrogen embrittlement in bearing steels, and the means by which manufacturers may optimise alloys and accompanying processes to prevent embrittlement. Notably, novel steels combining both high strength and hydrogen embrittlement resistance are reviewed with respect to their design, evaluation methods, and required future work.

The effects of neutron radiation on nickel-based alloys in thermal reactors are defying predictions that were made based upon accelerated testing in fast reactors. As nickel-based alloy components face significant doses in aging thermal reactors and their role in Gen-IV reactor designs becomes prominent, the literature on the effects of radiation on such alloys must be reviewed to enable better structural integrity assessments for relevant components and optimise alloys with respect to irradiation embrittlement resistance. This paper reviews the available data on the effects of radiation, notably neutron radiation, on nickel-based alloys and discusses the possible mitigation strategies and design opportunities for radiation embrittlement-resistant alloys based on recent developments in alloy computational design. This review was submitted as part of the 2016 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.

This is a transcript of the discussion session on the effects of hydrogen in the non-ferrous alloys of zirconium and titanium, which are anisotropic hydride-forming metals. The four talks focus on the hydrogen embrittlement mechanisms that affect zirconium and titanium components, which are respectively used in the nuclear and aerospace industries. Two specific mechanisms are delayed hydride cracking and stress corrosion cracking.This article is part of the themed issue 'The challenges of hydrogen and metals'.